<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        // +=,-=
        var a = 2;
        //a=a+4;
        a+=4;
        var b = 4;
        b-=4; // b=b-4;
        console.log(a)   // 6
        console.log(b)   // 0
    </script>
</body>
</html>